grab sample


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grab sample

In public health and medical statistics, a chaotic set of data from which conclusions are injudiciously drawn. Because the sample is not carefully randomized or scientifically selected, the conclusions derived from such sample groups may be inaccurate.
See also: sample

sample

1. a specimen of fluid, blood or tissue collected for analysis on the assumption that it represents the composition of the whole.
2. for statistical purposes a small collection of individual units taken from the population which is under investigation on the assumption that they represent the characteristics of the entire population.

EPSEM sample
acronym for 'equal opportunity of selection method'.
grab sample
sample of greasy wool taken at random by a special machine from each bale on the sale floor. Buyers price the bale on the basis of the appearance of the grab sample and the objective measurements.
multi-stage random sample
with very large populations it may be desirable to arrange the data into groups on one criterion, e.g. address by area of postcode, and to select randomly from within this group, then select from within this sample to obtain randomly a representative number of specimens, such as dogs of each age group.
random sample
the selection from a population of the units which are to constitute the sample of that population is made in such a way that each unit of the population has an equal chance of being selected. Called also simple random sample.
simple random sample
see random sample (above).
stratified random sample
the data is arranged into subsets or strata based on the possession of certain characteristics which are common to the members of the subset. The selection of units to comprise the sample of the parent population is arranged so that the proportional representation of each subset in the final sample fits a prearranged schedule.
volunteer sample
sample donated by interested parties; a biased sample because it does not represent all sections of the population. Called also self-selection.
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References in periodicals archive ?
Because grab samples were used for this evaluation, the authors would have been better served by evaluating unit performance by household, on the basis of four samples.
Analytical results reveal the vein to be strongly enriched in gold and silver with values of grab samples up to 44.
Grab samples have assayed up to 47g/t Au and 5560g/t Ag (PR 8/06/2005).
grab samples reported from the area (OGS Report 282, 1993) returned up to 2.
A group of 27 of 418 rock grab samples assayed between 0.